FOSSIL VERTEBRATES FROM SAN PEDRO VALLEY—GAZIN 48] 
Bensonomys arizonae 
(Gidley), n. gen. 
Onychomys bensoni Gidley 
Sigmodon medius Gidley 
Neotoma fossilis Gidley 
Lagomorpha 
Leporidae 
Hypolagus sp. 
Sylvilagus? bensonensis, 
n. sp. 
Leporid sp. 
Proboscidea 
Mastodontidae 
Cordillerion bensonensis 
(Gidley) 
Mastodont sp. 
Perissodactyla 
Equidae 
Nannippus cf. phlegon 
(Hay) 
Plesippus sp. 
Artiodactyla 
Tayassuidae 
Platygonus sp. 
Camelidae 
Camelid sp. 
Antilocapridae 
Antilocaprid sp., possibly 
Texoceros sp. 
Sigmodon curtisi Gidley 
Sigmodon minor Gidley 
Ondatra sp 
Lagomorpha 
Leporidae 
Lepus sp., near L. cali- 
fornicus Gray 
Sylvilagus sp., near S. 
floridanus (Allen) 
Proboscidea 
Mastodontidae 
Stegomastodon arizonae 
Gidley 
Perissodactyla 
Equidae 
Equus sp. 
Artiodactyla 
Camelidae 
Camelid sp. 
Tanupolama cf. longurio 
(Hay) 
Antilocapridae 
Cf. Capromeryx gidleyi 
Frick 
Cervidae 
Cf. Odocoileus sp. 
AGE AND ENVIRONMENT OF THE FAUNAS 
Gidley originally contended that both the Benson and Curtis ranch 
deposits were of late Pliocene age, based on what he considered to be 
a peculiar mingling of modern and more ancient forms. In 1926 
he tentatively assumed that the Benson fauna was slightly older 
than that of the Blanco, and the Curtis ranch assemblage was a little 
younger. It should be noted, moreover, that the Blanco at that time 
was regarded as about middle Pliocene in age. Gidley’s conclusions 
were arrived at under handicap, through lack of comparable faunas 
in other areas with which comparisons could be made, except for 
that of the Blanco with its dearth of smaller forms. He anticipated, 
however, that the San Pedro Valley faunas would eventually become 
standards of reference for the stages represented. 
The Benson fauna may well be equivalent in age to that of the 
Blanco, although the faunas are not strictly comparable, perhaps 
